Velocity at the Bottom of a Flow

We have made a device to measure the velocity of water at the bottom of a flow. This was done by making use of the force the water exerts on a rotating propeller. The rotational velocity then was used to compute the velocity of the flow itself. To measure the rotations the propeller made, a magnet detection sensor and magnets were used.

Supplies:

• Arduino Uno
• Laptop (including the program 'Arduino')
• Arduino wiring cables
• Power cable (USB to DC plug)
• LCD i2C display
• Breadboard
• PVC tube (1 [m] long, 70 [mm] diameter)
• 2 PVC end caps (for 70 [mm] diameter)
• Glue
• 5 plastic coffee spoons
• PMMA disk with 5 indents (if PMMA not available any tough material is acceptable if not absorbent for water)
• Bal bearing (10 [mm])
• 6 bolts (for 10 [mm])
• Thread (10 [mm])
• E49 Hall sensor
• 4 strong magnets
• Battery pack (DC plug)
• 6 AA batteries
• 2 wooden boards (any prefered size)
• PVC tube cut-out

Tools:

• Drill
• Glue pistol
• Pliers

The circuit is build as depicted in the picture. The display is connected to the breadboard for power and to the Arduino pins A4 and A5 for the display information transfer. The E49 Hall Sensor is connected to the breadboard for power as well, however the third wire of the sensor is connected to the A0 pin of the Arduino. Power is provided to the breadboard by two wires from the GND and 5V pins. The Arduino is subsequently connected to the battery pack, in which 6 AA batteries are to be placed.

(Since it was not possible to show a breadboard in the figure above two wires overlap. This thus can easily be solved by building the circuit with a breadboard and the instructions from above. The display is represented by the display component in the bottom right of the figure.)

Now the code is writen for the device. This was done using the program 'Arduino' on the laptop. Firstly, the code reads out the E49 Hall Sensor (INPUT) and these values are read out. Then a boolean statement is used to count the amount of rotations the propeller makes. Each time the magnets pass the Hall Sensor a value of 1 is added to the running count. To prevent the sensor to add multiple counts in a single rotations (due to magnetic fluctuations) an if statement is added. When a certain threshold is reached it stops, after which the code instructs the display to show the velocity of the flow. This velocity is computed using the radius of the propeller and the time passed to reach the threshold. Lastly, the code was uploaded to the Arduino.

The code we wrote is included below as a .ino file.

Thirdly, the main structure of the device is made. The PVC tube is to be connected to an PVC end cap and a wooden board, on which the circuit is placed. The PVC tube is connected to the end cap by pushing it on, while the wooden board is connected to the cap with glue.

The inside of the disk was glued to the ball bearing. This way the disk can rotate while it stays in its place on the thread. The coffee spoons were placed in the indents of the disk. These spoons are also connected with glue to the PMMA disk. Finally, on one side of the disk 1 magnet is placed and on the other side 3 are placed. These magnets are place such that they attract oneanother.

A hole is drilled in a PVC end cap with the size of the thread. The thread is then put through the hole and is fastened by a bolt on each side of the cap. Then a bolt is screwed on the thread (below the end cap) after which the propeller is screwed on as well. Afterwards, another bolt is used to fasten the ball bearing of the propeller. At the bottom of the thread a wooden board is placed to act as a stand, which can be placed at the bottom of the flow so the device can rest on it. This board is also fastened using the last two bolts. The lower structure is secured to the PCV tube by screwing it on.

Finally, a cut-out of a PVC tube can be used to 'shield' the coffee spoons on one side. This can be done to make the device perfomance better because there is less pressure on the convex side of the spoons. This means that the propeller can rotate more easily. This cut-out was placed using glue.